Intra-Set Rest Periods Boost Power (+38%) & Strength Gains (+65%) Without Hampering Skeletal Muscle Hypertrophy

Up your strength /check! Up your power /check! Up your muscle gains in the long term /likely!

Intra-Set Rest Periods? No, that's not identical to "clustering" or "cluster training", although it may appear as if it was. Ok, let's briefly summarize what IRS / clustering is: Basically the idea is to perform the exact same amount of reps and thus work with a heavier weight than usual to induce greater gains (usually strength gains). Now how can you do that? Well, one possibility would be to simply add another set, so that you would now be doing 4 set of 10 reps instead of the usual 3 sets of 10 reps. Unfortunately, this is yet nothing but another instance of the notorious more helps more approach of which you should by now have realized that it is pointless and ineffective.

Now things are getting a little complicated, because contrary to a classic clustering regimen, where you would add weight to the bar, do say 8 reps, take 10 breaths and rep out the other two, the intra-set rest (IRS) period protocol in the Oliver study employed a tightly controlled and not an "ad hoc" variety of "clustering". Contrary to the control group who performed a regular 4x10 routine, the IRS group broke their 4 sets of 10 with 120s rest between sets up to eight sets of five with only 60s of rest in-between the exercises (see table 1 for more details)

Table 1: Overview over the workout program (adapted based on Oliver 2013)

It's easy to see, there is no black magic involved. Same lifts, same plan, same progression, but different set x rep scheme and inter-set rest for the STD vs. ISR groups. In the fourth unloading week, tests were conducted and the same protocol was repeated with accordingly increased weights. All sessions were supervised and the compliance was 95% over the whole 3x4 week study period.

The participants of the study had all been doing upper + lower body resistance training for at least 2 years and were thus familiar with the basics of strength training, before the study they received nutritional counseling which is probably the reason that all of them increased their protein intake significantly (ca. +50g to ~190-200g/day; no inter-group difference).

The same goes for the changes in muscle fiber and body composition. All subjects experience an increase in MHC-IIa fibers (glycolytic) and gained lean mass continuously. Unfortunately, they also gained body fat, so that the body fat % (DEXA measured) did not change at all.

The power and strength advantage

What did however react to the modified rest times were the changes in strength and power on all the major lifts. According to Oliver, et al.

Table 2: Effect size and qual. inferences on intergroup difference; (t)rivial, s - (s)mall, (m)edium., (l)arge (Oilver. 2013).

"Only subjects in ISR experienced an increase [in 1RM bench press & squats] at 4, 8 and 12 weeks. This corresponded to greater increases at 4 (ISR, 6.6±6.6 kg; STD, -1.4±6.2 kg; p= 0.012), 8 (ISR, 9.9±6.8 kg; STD, 2.9±5.8 kg, p = 0.016) and 12 (ISR, 15.1±8.3 kg; STD, 9.1±3.7 kg; p = 0.051) weeks.

[...] Again, only ISR increased at 4, 8 and 12 weeks. Greater percent increase from baseline was observed in ISR at 4 and 8 weeks (p = 0.017 and 0.034, respectively), with 12 weeks approaching significance (p = 0.082)." (Oliver. 2013)

Similar differences were observed on the power output strength, where the group difference at both 8 weeks (ISR, 151.0±74.0 W; STD, 97.5±60.9 W; p = 0.084) and 12 weeks (ISR, 282.1±104.1 W; STD, 204.9±70.2 W; p = 0.063) approached significance with subjects in ISR showing a greater increase. Interestingly, the advantage became even more obvious, when the changes for normalized for the subjects' body weight (from p = 0.084 to p = 0.016 and p = 0.063 to p = 0.038 after 8 and 12 weeks, respectively - that means what may be at best a trend on an absolute level is a statistically significant advantage if you take the muscle mass into account, as well)

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Bottom line: It sure looks as if IRS would in fact be a viable training strategy for anyone training for muscle hypertrophy, strength and power. Neither the workload, nor the workout time changes and still the results improve. And I can hardly phrase it better than Oliver et al. did:

Suggested read: "Training for Size & Strength: Does Rest Matter? Study Finds 7-9% Greater Increase in Muscle Size With Decreasing Rest Periods." (read more)

"Based on these results, it could be suggested the incorporation of ISR in the hypertrophic phase of a traditional or non-traditional periodized training program would allow for greater improvements  in strength and power. 

Whether these improvements would result in greater gains in strength and power output over an entire mesocycle is unknown, but hypothetically entering the strength and power phases of a training mesocycle at higher performance ability (strength and power) would allow a continued improvement above that achieved during traditional training models." (Oliver. 2013)

What? Oh, yes... I will tell you if the researchers ever conduct this study. To be honest, I am yet pretty sure that this is not going to happen. After all, the results won't be patentable and since we are dealing with healthy people (worse athletes!) the governments of the Western Obesity Belt are more likely to burn a few additional millions to find new pharmacological methods to prolong the misery of the increasingly obese majority of their citizens - I mean, who would vote for them if they told people that we already had the solution to the obesity epidemic, but it was not available in convenient pill form?

References:

• Oliver JM, Jagim AR, Sanchez AC, Mardock MA, Kelly KA, Meredith HJ, Smith GL, Greenwood M, Parker JL, Riechman SE, Fluckey JD, Crouse SF, Kreider RB. Greater Gains In Strength And Power With Intra-Set Rest Intervals In Hypertrophic Training. J Strength Cond Res. 2013 Jun 3. [Epub ahead of print]